1. Field of the Invention
This invention pertains to the field of alert signals being provided to the pilot of an aircraft, where such signals are generated by a terrain awareness and warning system.
2. Description of the Related Art
Beginning in the early 1970's, a number of studies looked at the occurrence of “controlled flight into terrain” (CFIT)-type accidents, where a properly functioning airplane that is under the control of a fully qualified and certificated crew is flown into terrain (or water or obstacles) with no apparent awareness on the part of the crew. Findings from these studies indicated that many such accidents could have been avoided if a warning device called a ground proximity warning system (“GPWS”) was used. There have been numerous patents issued in the field of GPWS and related art. A sampling of patents issued in the art and related art include U.S. Pat. Nos. 5,839,080; 6,092,009; 6,122,570; 6,138,060; 6,219,592; 7,145,501; 7,908,045; and 8,019,491. A sampling of patents applications in the art and related art include U.S. patent application Ser. Nos. 11/904,491 and 11/904,492.
Advances in technology have permitted vendors and designers of avionics equipment to develop a newer type of GPWS that provides greater situational awareness for flight crews. The U.S. Federal Aviation Administration (“FAA”) has classified such systems as Terrain Awareness and Warning Systems (“TAWS”). The advancement of technologies—more precise navigation systems, increased computer memory storage, and better display technology—have allowed further development of the common features of TAWS: (1) use of airplane position information from the aircraft's navigation system(s), (2) an onboard terrain database, and (3) a means of displaying the surrounding terrain. Aircraft position information from the aircraft's navigation system is fed to a TAWS computer. The TAWS computer compares the airplane's current position and flight path with the terrain database associated with the system. If there is a potential threat of collision with terrain, the TAWS computer sends warning alerts to the airplane's audio system.
There are scenarios for which TAWS has been implemented. These scenarios may be categorized by the flight operations in which aircraft accidents have occurred: departure operations, enroute operations, and arrival operations. First, departure operations could include accidents in which the aircraft does not climb fast enough to clear a terrain cell of interest and in which a pilot has leveled off before the aircraft has achieved the appropriate altitude to clear the terrain. Second, enroute operations could include accidents associated with level flight into terrain and descending flight into terrain. Third, arrival operations could include accidents associated with premature descents and late level-offs in a step down arrival procedure. The embodiments disclosed herein present novel and non-trivial systems and methods which address these scenarios.